Automatic electric toaster



Feb. 18, 1947. o v 2,415,963

v AUTOMATIC ELECTRIC TOASTER Filed Jan. 51, 1945 3 Sheets-Sheet 1 A9 j j Feb. 18, 1947. OLVING 2,415,963

AUTOMATI C ELECTRIC TOASTER Filed Jan 51, 1945 3 Sheets-Sheet 2 73 y j/ I 1 Feb. 18, 1947.

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B. G. OLVING AUTOMATIC ELECTRIC TOASTER F iled Jan. 51, 1945 3 Sheets-Sheet 3 Patented Feb. 18, 1947 AUTOMATIC ELECTRIC TOASTER Bror G. Olving, Elgin, Ill., assignor to McGraw Electric Company, Elgin, 111., a corporation of Delaware Application January 31, 1945, Serial No. 575,471

6 Claims.

My invention relates to automatic electric toasters and particularly to timing means for such toasters to predetermine the length of a toasting cycle.

An object of my invention is to provide a timing means and an electric circuit therefor which are dependable and which will stand up in service for a long time.

Another object of my invention is to provide a timing means, the performance of which depends upon the inherent electrical characteristics of its component parts and the operation of which is not dependent upon nor controlled by any energy supplied from mechanical or thermal storage devices.

Another object of my invention is to provide a timing means and an electric circuit therefor, including an electron tube to obtain the abovementioned performance.

Other objects of my invention will either be apparent from a description of several modifications of circuits embodying my invention or will be pointed out in the course of such description and set forth particularly in the appended claims.

In'the drawings,

Figure 1 is a side elevational view of a toaster having operatively associated therewith a system embodying my invention,

Fig. 2 is a front elevational view of the toaster, Figs. 1 and 2 being on a reduced scale,

Fig. 3 is a longitudinal, vertical, sectional view through a toaster having associated therewith a circuit embodying my invention,

.Fig. 4 is a vertical, lateral, sectional view therethrough taken on the line 4-4 of Fig. 3,

Fig. 5 is a fragmentary horizontal, sectional view taken on the line 5-5 of Fig. 4,

Fig. 6 is a bottom view of a timing element comprising a part of my invention,

Fig. 7 is an end view of the parts shown in Fig. 6, and,

Figs. 8 and 9 are two different diagrams of connections embodying my invention.

I provide further a plurality of toast heating u elements 2| here shown as four in number; that is, I provide a pair of planar vertical toast heating elements for each of two toasting chambers comprised in a two-slice toaster. I

Each toast heating element 2| includes one or more sheets 23 of electric-insulating material, such as mica, on which is wound a strand 25 of a suitable and proper resistor material now well known in the art. I provide further a plurality of vertically extending guard and guide wires 21 on each side of the toasting chambers in order to insure that a slice of bread placed in a toasting chamber will be evenly toasted on both sides by the simultaneous application of radiant and convected heat from the pair of toast heating elements 2|. The guard wires 21 may be suspended from top frame plates 29 which extend longitudinally of the toaster. I provide further a rear intermediate wall 3| as well as a front intermediate wall 33. These rear and front intermediate Walls cooperate with one of the inner toast heating elements 2| and an outer baflle plate 35 to constitute a toasting chamber.

The method and means for holding all of the hereinbefore enumerated parts in proper operative position relatively to each other are all old and well known in the art.

I provide also a pair of bread carriers 31 which are adapted to be vertically movable in each of the toasting chambers from a top or non-toasting position to a lower or toasting position. The rear end portion of each of the bread carriers extends outwardly through a vertical slot in the rear intermediate wall 3| while the front end portion extends through a vertical slot in the front intermediate wall 33. Since it is desired to normally yieldingly maintain the bread carriers in their upper or non-toasting position, a tension coil spring 39 is provided, the upper end of which engages a lug 4| secured against the front surface of the front intermediate wall 33 while the lower end thereof engages a rearwardly extending lug 43 constituting a part of a rear carriage plate 45. Rear carriage plate 45 is provided with two rearwardly extending extensions 41 to which the front end portions of the bread carriers 31 may be secured in a manner well known in the art. The coil spring 39 is therefore effective to yieldingly hold the bread carriers 3'! in their upper non-toasting position.

Means for causing downward movement of the bread carriers comprises a front carriage plate 49 which is spaced from the rear carriage plate 45 by a plurality of headed studs 5| having thereon a plurality of externally grooved rollers 53 positioned between the rear and the front carriage plates. Each of the grooved rollers 53 is rotatably mounted on its stud 5i and may engage the inner surface of vertically extending rods 55, the lower ends of which are secured in the front portion of base plate I5 while the upper ends thereof are held by interengagement with the forward portions of the top frame p1ates29, A cross bar 5? is also provided to hold the upper end portions of the rods 55 as well as the front end portions of the top frame plates 29 in properly spaced positions so that the bread carrier can be moved easily and quickly from the upper nontoasting position to their lower toasting position.

Means for controlling the energization of the four toast heating elements 2 comprises a pair of fixed contacts 59 and SI which are supported as by a block 63 of electric-insulating material which is, by turn, upported by a bracket 65 secured to the front surface of the front intermediate wall 33 a jacent the lower end portion thereof, I provide a contact bridging member 51 which is insulatedly mounted on and supported by a bracket t9secured tot'he front. carriage plate d3. 1 Th front carriage plate .33 has a forwardly extending bar "iI secured thereagainst, the forward end of the said bar extending through a slot in the front wall of the outer casing I? and has an actuating'knob 13 mounted thereon outside of the cas n Ililprovide also a second pair of fixed contacts [5 and 'Il which are mounted on a block I3 of electric-insulating material which may be supported by a bracket BI .secured'against the front Surface of .the front intermediate wall 33 adjacent the upper end portion thereof. It is to be understood that contact bridging member El is in close engagement with the upper fixed contacts l5 and 11 when the bread carriers are in their raised or upperpositionand that it is in close operative engagement withcontacts 53 and ti when the bread carriers have been moved downwardly to their lower or toasting-position.

.Means for holding the bread carriers in their lower or toasting position comprises a hook 153 which is mounted on the lower end of a resilient bar-5, the upper end of which is secured against a projection ill at'the upper right hand side of the front carriage plate 43. Resilient bar 35 is .biased in a. clockwise direction against a stop 83 which is just above .the hook 355. When the breadcarriersare moved to their lower or toastm position, hook 83 will engage with the hookshapedend SI of a latch comprising in addition to the hook-shaped-end 9! of a vertical arm 93, a substantially horizontally extending arm 95 integral with-arm 93 and pivotally supported as by ,a lug or bracket v3i secured against the lower surface of a plate 99 which is, in turn, secured against the lower surface of bottom plate I5 by a7plurality of short machine screws IilI. An

armature core I33 is pivotally mounted on-the free end of arm 95 and extends upwardly into a coil .105 constituting a part of the latch release mechanism to be hereinafter described. A small condenser I! is connected across the terminals ,of coilIil to prevent chattering.

It is to be understood that substantially all of the parts hereinbefore described are old and well known in the art and constitute no part of my present invention now to be described.

I provide a pair of supply circuit conductors III and H3, conductor Ill being connected to of resistor H5 being connected to one terminal of one toast heating element BI which I have shown as being connected in series electric circuit in pairs relatively to each other. The other free terminal of the second toast heating'element is connected by a conductor Ill to the upper fixed contact I5. Supply circuit conductor I!3 isconnected by a conductor I if! to the lower fixed contact 5i while the lower fixed contact 59 is connected by a conductor IZI with the upper fixed contact 15.

I provide an electron tube I23 having therein a heated filament I25, which filament is heated by a resistor H5 through conductors I21 and I29. The tube I23 includes also an indirectly heated cathode l3I, a plate anode I33, a grid I35, as well asa shield grid I31.

I provide also an adjustable potentiometer I33 having manually-adjustable contact arm I ll, the potentiometer comprising a part of a voltage divider I43 with which thepotentiometer is,connected in series electric circuit. The ohmic resistance of the potentiometer I33 is on the order of 500 ohms while the total resistance of the voltage divider I 43 may been the order of 3000 ohms. I provide further a ballast condenser I45 which is connected in parallel circuit relative to a part of the voltage divider I43, the potentiometer I33, and anotherportion I41 of the voltage divider. The lower terminal of the resistor I41, the ohmic resistance ,of which is on the order of 300 ohms, is connected to a conductor I43 which connects conductor I21 to the screen grid I31. The upper terminal of the voltage divider I43 is connected by a conductor I5I to one terminal of a half-wave dry-type rectifier I53, the other terminal of which is connected to conductor I2I. I provide further a timing resistor I which has a negative temperature coefficient of resistance and which is so positioned in a toaster as to be subjecttoradiant heat from oneor more of the toast heating elements..2I or is positioned in a toasting chamber .itself. One terminal of the timing resistor I55, the ohmic resistance of which is on the order of 10 megohms, is connected by a conductor I51 to the upper fixed contact 11. The other terminal of .the timing resistor I55 is con.- nected to the adjustable contact arm MI by a conductor I59.

I provide furthera timing condenser I=6I, one terminal of which is connectedto aconductor I63 whichconnects the upper end of the small resistor IN to the lower terminal .of potentiometer I39 and to the indirectly heated cathode I3I. The

, function of the small resistor is to give a small negative bias to the cathode I3 I The upper fixed contact TI is connected by aconductor I65 to the other terminal of the timing condenser I6I as well as to the left hand terminal of a current limiting resistor 161 which is connected in series circuit with the grid I35. The resistance of resistor I61 maybe on the order of 50,000 ohms. The plate anode I33 is connected to one terminal of the coil I05 of the latch release means by a conductor I69 while aconductor Ill connects the other terminal of coil I to conductor I5I.

It is to be understood that the resistance of resistor H5 is suificient to properly energize the heated filament I25 of the electron tube I23.

Let it now be assumed thatman operator desirestotoast one or two slices of bread which he will drop upon the bread carriers in the toaster when they are in their upper or non-toasting positions. After placingthe slices of bread onsthe bread carriers, he will then press downwardly on knob I3 moving the bread carriers into their lower or toasting positions where they will be held by interengagement of hook 83 with hook III. The engagement of contact bridging member 61 with the lower fixed contacts 59 and 6| energizes the toast heating elements 2| as well as the resistor H5 and also the rectifier I53. Let it now be assumed that the operator desires to obtain a slice or slices of bread toasted to a medium degree with the contact arm MI in substantially the position shown in Fig. 8 of the drawings. The energized rectifier I 53 will impress half waves of direct current voltage generated by it upon the voltage divider I43, the potentiometer I 39, as well as the small resistor Ill, the voltage applied to the voltage divider I43 and the potentiometer I39 and the resistor I41 being substantially equal to the peak value of the voltage provided by the alternating current circuit comprising conductors II I and II 3.

The contact arm I 4| will provide a predetermined but-lower voltage than that provided by the rectifier I53, upon the timing resistor I55 as well as upon the timing condenser I 6|. The voltage applied to the condenser I6I will be sufiicient to charge the same to a voltage high enough to cause firing of tube I23 after a length of time on the order of 2% or 3 minutes, when the potential applied to the indirectly heated cathode I3I and the grid I35 will be high enough to cause firing of the tube I23; that is, will cause the tube to become conducting. The current traversing the tube I23 is supplied by the conductors II I and I I 3, through circuit substantially as follows: from conductor III, through conductor I 21, cathode I3I, plate I33, conductor I69, coil I05, conductor 'III, rectifier I53, conductor I2I, closed main switch and through conductor II9 to the second supply circuit conductor H3, and when this current traverses the tube, it will also traverse the coil I05 of the electromagnetic latch release means with the result of quick upward movement of core I03 and attendant disengagement of hook end 9I from hook 83 and quick upward movement of the bread carriers from their toasting position into their upper or non-toasting position.

As has already been hereinbefore set forth, the

characteristic of the timing resistor I55 is that it has a negative temperature coefi'icient of resistance, that is, the resistance of resistor I55 decreases upon an increase of temperature thereof.

This lowered resistance causes a quicker charging of the timing condenser I5I than heretofore with the result that the potential across the terminals of timing condenser IBI will reach a value sufliciently high to cause firing of tube I23 in a shorter time than Was the case during the first or cold operation of the toaster and of tube I23. It is only necessary to properly correlate the resistance of timing resistor I55, the negative temperature coefficient of resistance thereof and the characteristic of the electron tube I23 in order to obtain a proper cooperative effect of all of these parts with the result that substantially the same degree of toasting will be obtained in quickly successive toasting operations irrespective of the change of temperature of the toasting structure, and, therefore, of the timing resistor I55.

When it is desired to vary the degree of toasting to be effected, it is only necessary to move contact arm I4I manually before the start of a toasting operation. Thus when arm MI is moved in a clockwise direction, a lighter piece of toast will be obtained as a higher voltage is impressed on the -'-condenser charging circuit and the timing condenser'will be charged to the tube firing potential in a shorter time and conversely if contact arm I4! is moved in a counter-clockwise direction a darker piece of toast will be obtained, as a lower voltage will be impressed from the potentiometer on the condenser charging circuit and a longer time period will be required to charge the condenser to the tube firing potential. It is to be understood that the duration of a toasting operation will vary with a change in the position of the contact arm I4I; that is, when arm MI is moved in a clockwise direction, a shorter toasting period will result While if it is moved in a counterclockwise direction, a longer period of operation will result.

The use of a timing resistor I 55 having a negative temperature coefiicient of resistance also effects automatically, a compensation for varying line circuit voltages as the temperature of the toast heating elements 2I will increase when subject to an increased line circuit voltage with the result that the temperature of the timin resistor I55 is also increased with the attendant result that its resistance is still more greatly decreased. The result of this greater decrease in the resistance is that the time period of a toasting operation is also decreased thereby resulting in substantially the same degree of toasting but in a relatively shorter period of time.

The provision of the upper fixed pair of contacts I5 and TI provides a means for effecting discharge of the condenser IBI through the toast heating elements 2| when the contact bridging member 67 is moved upwardly into engagement therewith, through a circuit comprising resistor IE5, the pair of toast heating elements 2| conductor II'i', through fixed contact members I5, Ii and contact bridging member 61, through conductor I65, through condenser I6 I, through a part of conductor I63, through resistor I41, and then through conductor I2'I to the other terminal of resistor II 5. The condition of condenser IGI is therefore substantially the same after each separate time of operation with the result that the timin cycles provided by the system shown in Fig. 8 will always be initially the same as has hereinbefore been described.

Referring now to Fig. 9 of the drawings, I have there shown a modification of a circuit embodying my invention in which I employ a cold cathode electron tube I8I which has a plate anode I83, 9, control grid I85, and a cold cathode I81. This tube is inherently of the positive gridcontrolled voltage type requiring a positive potential of volts between the control grid and the cathode before firing when a D. C. voltage in the neighborhood of volts is employed between the anode and the cathode.

I provide an electromagnetic latch release comprising an armature coil I05, an armature core I03, as well as an intermediate relay comprising an armature coil I89, an armature core I9I having insulatedly connected therewith a contact bridging member I 93 which is adapted to be engaged with and disengaged from a pair of fixed contacts I94 and I95.

I provide also a potentiometer I 39 having a manually-adjustable contact arm I4I which is electrically connected by a conductor I59 to one terminal of a timing resistor I55 which has a negative temperature coeflicient of resistance and an ohmic resistance, when cold, on the order of 10 megohms. A single half-wave dry-type rectifier I53 is connected between conductor I2I and a conductor I91 which extends from the upper garages terminal of coil. I89 of the intermediate relay to one terminal of a small current limiting resistor I99. having an ohmic resistance on the order of 300 ohms. The-other terminal of resistor I99 is connected to one terminal of the potentiometer I39, the other terminal of which is connected to a conductor 2M which extends fromsupply circuit conductor I I I to fixed contact I95 as well as to the cold cathode I81. A filter or ballast condenser I45 is connected in shunt circuit relatively to the potentiometer I39 while a timing condenser IBI is connected between conductor 20I and a conductor 293., the other terminalof which is. connected to; the lower terminal of timing resistor I55. The other terminal of the electromagnetic coil I89 is connected by a conductor 205 to plate anode I83. The grid I85 is connected to a, current limiting resistor 29?, the ohmic value of which is on the order of 10,000 ohms, and has its other terminal connected to conductor 203. A small condenser 20.9 is connected in shunt circuit with coil I to prevent chattering.

Let it now be assumed that an operator desires to toast one or two slices of bread, starting with a cold toasting structure. Contact arm MI may be set in substantially the position shown in Fig. 9 of the drawings to obtain a medium degree of toasting in a toasting cycle, the length of which is on the order of 2 /2 to 3 minutes. The voltage impressed upon the timing resistor I55 and through it upon the timing condenser IGI is such that the potential across the terminals of condenser IEI will be raised to a value suificiently high to cause firing of tube I8I in a length of time on the order of 2 /2 to 3 minutes. When the tube fires, coil I89 is traversed by a relatively small current causing quick upward movement of armature core I9I and engagement of the contact bridging member I93 with the fixed contacts I95 and I9 5. This causes a current to traverse coil I05 of the electromagnetic latch release means with consequent quick upward movement of armature core is? and attendant disengagement of hook end 9I from hook 83 with resultant quick upward movement of the bread carriers intotheir upper non-toasting positions.

Substantially the same comments as made hereinbefore in connection with potentiometer I39 and the timing resistor I55 shown in Fig. 8 apply equally well to Fig. 9 insofar as obtaining substantially the same degree of toasting with changing temperature of the toaster structure and with obtaining different degrees of toasting as may be desired by an operator.

When contact bridging member 6'! is moved into engagement with fixed contacts I5 and 11 the timing condenser I6I is discharged through the two toast heating elements 2I whereby a fully discharged timing condenser results preparatory to any further toasting operation.

Various modifications may be made in the systems embodying my invention without departing from the spirit and scope thereof and all such modifications thereof clearly covered by the appended claims are to be considered as part of my invention.

I claim as my invention:

1. In an automatic electric toaster, the combination with a toasting chamber having electric toast heating means therein adapted to be connected to an A. C. supply circuit and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, and a rectifier connected in series cir- 'cuit.;with each other and across the supply .cir-

cuit, av timing condenser and a timing resistor energized by: said potentiometer tov increase the potential of the condenser gradually, an electron tube connected to said: condenser and adapted to be fired thereby, means energized-by the current traversing the tube when fired for causing termination of a toasting operation, said timing resistor being positioned in the toasting chamber and having a negative temperature coefiicient of resistance tov cause substantially uniform toasting of successive slices of bread irrespective of temperature change of the toaster and means for causing discharge of said condenser through the toast heating elements after the termination of the toasting operation.

2. In an automatic electrictoaster, the combination with a toasting chamber having electric toast heating means therein adapted to be connected to an A. C. supply circuit and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, and a rectifier connected i Series circuit with each other and across the supply circuit, a timing condenser and a timing resistor energized by said potentiometer to increase the potential of the condenser gradually, an electron tube connected to said condenser and adapted to be fired thereby, means energized by the current traversing the tube when fired for causing termination of a toasting operation, said timing resistor being positioned in the toasting chamber and having a negative temperature coefiicient of resistance to cause substantially uniform toasting of successive slices of bread irrespective of changes of voltage of thesupply circuit, said potentiometer being manually-adjustable to vary the charging voltage applied to the timing condenser circuit to preset the degree of toasting of a sliceof bread, and means for causing discharge of said condenser through the toast heating elements after the termination of the toasting operation.

3. In an automatic electric toaster, the combination with a toasting chamber having electric toast heating means therein adapted to be connected to an A. C. supply circuit and means for starting a toasting operation, of means for terminating a toasting operation comprising a potentiometer, an a rectifier connected in series circuit with each other and across the supply circuit, a timing condenser and a timing resistor energized by said potentiometer to increase the potential of the condenser gradually, an electron tube connected to said condenser and adapted to be fired thereby, means energized by the current traversing the tube when fired for causing termination of a toasting operation, said timing resistor being positioned in the toasting chamber and having a negative temperature coeificient of resistance to cause substantially uniform toasting of successive slices of bread irrespective of temperature change of the toaster, said potentiometer being manually-adjustable to vary the voltage applied to the timing condenser circuit to preset the degree of toasting of a slice of bread, and means for causing discharge of said condenser through. the toast heating elements after the termination of the toasting operation.

4. In an automatic electric toaster, the combination with a toasting chamber, electric toast heating means therein adapted to be energized from an ,A. C. circuit, a control switch for the toasting operation and a releasable latch for holding the switch in closed position, of means for causing release of said latch to terminate a toasting operation comprising a potentiometer and a rectifier connected in series circuit with each other across the supply circuit, a timing condenser and a timing resistor energized by said potentiometer to gradually increase the potential of the condenser, an electron tube connected to said condenser and adapted to be fired thereby, means energized by the current traversing the tube for efiecting release of the latch, said timing resistor being positioned in the toasting chamber and having a negative temperature coefficient of resistance to cause substantially uniform toasting of successive slices of bread irrespective of temperature change of the toaster, said potentiometer being manually-adjustable to vary the voltage applied to the timing condenser circuit to preset the degree of toasting of a slice of bread and means including said contact bridging member for causing discharge of said condenser through the toast heating elements after the termination of a toasting operation.

5. In an automatic electric toaster, the combination with a toasting chamber, electric toast heating means therein adapted to be energized from an A. C. circuit, a control switch for the heating means biased to open position and including a contact bridging member, a bread carrier movable into toasting and non-toasting position and biased into non-toasting position, means to move the switch into closed position and said carrier into toasting position and a releasable latch for holding the switch in closed position and the carrier in toasting position, of means for causing release of said latch to terminate a toasting operation comprising a potentiometer and a rectifier connected in series circuit with each other across the supply circuit, a timing condenser and a timing resistor energized by said potentiometer to gradually increase the potential of thecondenser, an electron tube connected to said condenser and adapted to be fired thereby, means energized by the current traversing the tube for eflecting release of the latch, said timing resistor being positioned in the toasting chamber and having a negative temperature coefficient of resistance to cause substantially uniform toasting of successive slices of bread irrespective of temperature change of the toaster, said potentiometer being manuallyadiustable to vary the voltage applied to the timing condenser circuit to preset the degree of toasting of a slice of bread and means including said contact bridging member for causing discharge of said condenser through the toast heating elements after the termination of a toasting operation.

6. In an automatic electric toaster, the con bination with a toasting chamber, electric toast heating elements therein adapted to be energized from an A. C. circuit, a control switch for the heating elements biased to open position and including a contact bridging member, a bread carrier movable into toasting and non-toasting positions and biased into non-toasting position, means to move the switch into closed position and said carrier into toasting position, an electromagnetically-releasable latch for holding said switch in closed position and said carrier in toasting position, of means for causing release of said latch to terminate a toasting operation, comprising a potentiometer, a voltage divider and a half-wave dry-type rectifier connected in series circuit across the A. C. circuit, a timing resistor and a timing condenser connected to be energized by said potentiometer to graduallyincrease the potential of the condenser, a hot cathode normally non-conducting electron tube connected to the condenser and adapted to be fired thereby, said timing resistor being subject to heat from the heating elements, and having a negative temperature coefiicient of resistance to cause substantially uniform toasting of successive slices of bread irrespective of changes of temperature of the toaster, said potentiometer being manually-adjustable to preset the duration of a toasting operation and thereby the degree of toasting of a slice of bread, the current traversing said tube being derived from said A. C. circuit and through said rectifier and the coil of said electromagnetic release and means including the contact bridging member for causing discharge of the timing condenser through the toast heating elements and a part of said voltage divider at the termination of a toasting operation.

BROR G. OLVING.

REFERENCES CITED The following references are of record in the file of this patent: 

